Ditto
It is; for the latter, you just have to click "edit" and then grep the text for the post you want to put yours after. Here, because of the new rule about how "you're supposed to reply to the first post, not the previous one" (a remark of yours which, thanks to this new interface, I cannot diff-link to; another reason we should not adopt this, lest we give the Conservapedians ideas), you have to scroll up and down until you find the correct "first post."
Also, why do I have to hunt up and down the page and click an "Update" link before I am able to see my own posts?
So this is, by your own admission, buggy? That would rule it out for site-wide use immediately.
Yes, since it's alpha quality software. I have never denied that. I may have been too optimistic about the timeframe of LQT's maturation before, but right now the only reason it's installed at all is that I've managed to fix rollback on comments. Also, changing every talk page to lqt would be a huge job, we'd have to archive and clean up every talk page.
Right now, it's just here for testing, and if you like it you can enable it on your talk page.
That's why I said it needs a post new comment button at the bottom.
As for difflinks - each comment is actually a separate page. In the "More" dropdown menu you'll find a "link to" button, which will take you to the comment page: Thread:Forum:Use liquid threads in the forum?/Ditto/reply_(18)
What would be nice is a quote feature like most phpBB have.